A "like" on Facebook is worth a lot to advertisers there. Now it's also worth something to advertisers in other mobile apps.

Facebook's having a coming-out party for its "audience network," an ad network that lets existing advertisers on Facebook also have their ads placed in a large number of apps outside Facebook. The system stands to let Facebook reap even more lucrative rewards in mobile advertising, where it already makes the bulk of its revenue.

Through the network, any of Facebook's 1.5 million active advertisers can opt to have their campaign extended to other participating mobile apps. Facebook then places that company's ads in other publishers' or developers' apps, if Facebook determines it would be relevant to users there.

The ads will be placed by leveraging Facebook's massive collection of user data, including people's demographic information and their "likes" and interests on Facebook. It's part of a larger play by Facebook to grow its business on mobile by taking the targeting methods it already uses to show ads to users and applying them to other companies' apps.

"As a company, we've put a lot of effort into figuring out how to help developers manage the transition to mobile, and specifically the transition to mobile apps," said Sriram Kirshnan, product manager and head of mobile monetization at Facebook, in an interview.

The beta launch of Facebook's audience network came earlier this year at its F8 conference for developers, and until now only a handful of advertisers and app publishers participated. Now it's broadly available to app developers and publishers.

For example, a company can have its ads placed inside the Shazam music app, or the Huffington Post app, for Facebook users who may be interested in that company's product.

The connections between users and advertisers are made by the ad identifiers on people's mobile devices, Facebook says. "When you open an app that has Facebook ads, the app will let us know that it is looking to show you an ad and ask Facebook if we have an ad you might like to see," a company spokeswoman said.

Facebook says the matches are made anonymously. The company also stresses that no new forms of targeting are taking place for the technology to work.

Still, any broader leveraging of Facebook data is bound to raise privacy concerns among some people. Similar questions around privacy arose last week with the rollout of Facebook's Atlas ad server. Atlas also uses Facebook data to deliver ads outside the social network, though those ads may not appear on Facebook at all.

For the mobile audience network, Facebook says it's seen positive results in early tests with advertisers including Walgreens and publisher HarperCollins. The company also says it's paid out "millions" from advertisers to partners in the network. Facebook keeps a cut of the money it gets for ads that appear in other apps, but it wouldn't say what percentage it keeps.